Optical waveguide and optical transmitting/receiving module

ABSTRACT

To provide an optical waveguide and an optical transmitting and receiving module able to perform a transmitting operation and a receiving operation simultaneously, wherein a linearly first waveguide  21  that one side is coupled to an optical fiber  3  and the other side is coupled to a light receiving element  4 , and a second waveguide  22  that one side is coupled so as to make an acute angle θ with the side of the first waveguide  21  to be coupled to the light receiving element  4  and the other is coupled to a light emitting element  5  are provided. By controlling a shape of the second waveguide  22 , the receiving signal light from the optical fiber  3  is received to the light receiving element  4 , and is not guided to the second waveguide  22 . Therefore, the receiving operation and the transmitting operation can be preformed at the same time. Namely, when the transmitting optical signal is the incident of light from the light emitting element  5  to the second waveguide  22 , the optical signal is guided by the second waveguide  22  toward the first waveguide  21 , coupled to the first waveguide  21 , and guided toward the optical fiber  3.

TECHNICAL FIELD

The present invention relates to an optical waveguide and an opticaltransmitting and receiving module, particularly relates to an opticalwaveguide connecting an optical fiber and an optical element and anoptical transmitting and receiving module being provided with the same.

BACKGROUND ART

In recent year, in order that an optical module used to an opticalaccess system may make a size smaller and a cost reduce, an applicationof an optical transmitting and receiving module in which a transmittingoperation and a receiving operation are performed together by using anoptical waveguide etc. has been in main current. As the background ofthis, an expansion of a data transmission capacity has been demanded bysupporting explosive popularization of the internet. The opticaltransmitting and receiving module is mounted with both a light emittingelement for transmitting light and a light receiving element forreceiving light.

In an optical transmitting and receiving module in related art, anoptical signal transmitted from an optical fiber is divided by aY-branching waveguide and transferred to the respective light receivingelement and light emitting element (for example, refer to JapaneseUnexamined Patent Publication (Kokai) No. 2000-206349 and No.2002-169043).

Further, the optical transmitting and receiving module which the opticalsignal received from the optical fiber is transferred via a wavelengthselection filter only to the light receiving element has been proposed(for example, refer to Japanese Unexamined Patent Publication (Kokai)No. 2001-133642).

In the optical transmitting and receiving module mentioned in theJapanese Unexamined Patent-Publication (Kokai) No. 2000-206349 and No.2002-169043, by using the Y-branching waveguide, the optical signaltransmitted from the optical fiber is guided to two-branched waveguidesin a ratio of one to one respectively. Therefore, when the opticalsignal is received by the light receiving element, the optical signal isguided to the light emitting element simultaneously. Consequently theoptical transmitting and receiving module is not able to transmit theoptical signal simultaneously with receiving the optical signal.

The optical transmitting and receiving module mentioned in the JapaneseUnexamined Patent Publication (Kokai) No. 2001-133642) can performsimultaneously a transmitting operation and a receiving operation,however the module has to be mounted with a wavelength selection filteror other optical element, so that it has a disadvantage in terms of acost and productivity.

DISCLOSURE OF THE INVENTION

The present invention has as its object to provide an optical waveguideable to perform simultaneously a transmitting operation and a receivingoperation free from other optical element, and an optical transmittingand receiving module for the same.

To attain the above object, the optical waveguide of the presentinvention has: a first waveguide having a common transmitting andreceiving port at one side and a receiving port at the other side,extending linearly, and able to guide an optical signal in bi-direction;and a second waveguide branching off from the first waveguide so as tomake an acute angle with the receiving port, coupling to the firstwaveguide at one side, having a transmitting port at the other side, andguiding an optical signal to the first waveguide.

According to the optical waveguide of the present invention, theincidence optical signal from the common transmitting and receiving portis guided by the first waveguide to reach the receiving port. The firstwaveguide is extended linearly, so that the first waveguide almostguides the incidence optical signal from the common transmitting andreceiving port to the receiving port, and does not guide it to thesecond waveguide. Therefore, while the common transmitting and receivingport performs an incidence of the optical signal, the transmitting portof the second waveguide can perform the incidence of the optical signal.

The incidence light from the transmitting port of the second waveguideis guided toward the first waveguide, coupled to the first waveguide,and guided to the common transmitting and receiving port. The secondwaveguide is branched off from the first wave guide so as to make anacute angle with the receiving port, so that the light is not guided tothe receiving port side and the optical signal guided from the secondwaveguide is guided to the common transmitting and receiving port of thefirst waveguide.

To attain the above object, the optical transmitting and receivingmodule of the present invention in which a optical fiber, a lightemitting element and a light receiving element are coupled via anoptical waveguide has: a first waveguide coupling to the optical fiberat one side and a light receiving element at the other side andextending linearly; and a second waveguide branching off from the firstwaveguide so as to make an acute angle with the other side of the firstwaveguide and coupling the first waveguide at one side and a lightemitting element at the other side.

According to the optical transmitting and receiving module of thepresent invention, when the optical fiber performs the incidence of theoptical signal in the first waveguide, the optical signal is guided bythe first waveguide and received by the light receiving element. Thefirst waveguide is extended linearly, so that the incidence light fromthe optical fiber is almost received by the light receiving element andis not guided to the second waveguide. Therefore, while the opticalfiber performs the incidence of the optical signal, the light emittingelement can perform the incidence of the optical signal to the secondwaveguide.

When the light emitting element performs the incidence of the opticalsignal in the second waveguide, the optical signal is guided toward thefirst waveguide by the second waveguide, coupled to the first waveguideand guided toward the optical fiber.

The second waveguide is branched off so as to make an acute angle withthe other side of the first waveguide, so that the optical signal is notguided to the receiving port which is coupled to the other side of thefirst waveguide and the optical signal guided by the second waveguide isalmost guided to the optical fiber side of the first waveguide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plane view of an example of a configuration of an opticaltransmitting and receiving module having an optical waveguide accordingto the present embodiment.

FIG. 2 is a cross-sectional view along a line A-A′ of the opticalwaveguide in FIG. 1.

FIG. 3A is a view of a waveguide shape and FIG. 3B is a view of asimulation result of an intensity pattern of guided light in a receivingoperation by the optical waveguide shown in FIG. 3A.

FIG. 4A is a view of a waveguide shape and FIG. 4B is a view of asimulation result of an intensity pattern of guided light in atransmitting operation by the optical waveguide shown in FIG. 4A.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of an optical waveguide and an opticaltransmitting and receiving module according to the present inventionwill be described with reference to the drawings.

FIG. 1 is a plane view of an example of a configuration of an opticaltransmitting and receiving module having an optical waveguide accordingto the present embodiment. And FIG. 2 is a cross-sectional view along aline A-A′ of the optical waveguide shown in FIG. 1.

The optical transmitting and receiving module shown in FIG. 1 has anoptical waveguide 2 formed on a substrate 1 of a silicon substrate orsapphire substrate, an optical fiber 3, a light receiving element 4 anda light emitting element 5 which are mounted on the substrate 1.

The optical waveguide 2 has a first waveguide core portion (a firstwaveguide) 21 extended linearly and a second waveguide core portion (asecond waveguide) 22 that one side is coupled so as to make an angle θwith the first waveguide core portion 21. As shown in thecross-sectional view of FIG. 2, the respective waveguide core portions21 and 22 are formed on a cladding portion 20 which is formed on thesubstrate 1. Further, a cladding portion 23 is formed so as to cover therespective waveguide core portions 21 and 22.

The first waveguide core portion 21 has a common transmitting andreceiving port 21 a at one side and a receiving port 21 b at the otherside, and guides the optical signal in bi-direction. The first waveguidecore portion 21 is preferably a multimode waveguide and formed with adiameter of 50 μm, for example. In other words, in order to couple theoptical signal in low-loss guided from the second waveguide core portion22 which is branched off obliquely to guide it to the commontransmitting and receiving port 21 a, it is preferably that the firstwaveguide core portion 21 is a multimode waveguide having a largediameter and an incidence of light in easily. The multimode waveguide isdefined as a waveguide having a dimension able to guide a plurality ofmodes of the optical signal (passing ways of light).

The second waveguide core portion 22 is formed with a branching portion22 a by coupling one side so as to make the angle θ with the firstwaveguide core portion 21 of the receiving port 21 b side, and with atransmitting port 22 b at the other side. The angle and dimensions ofthe second waveguide core portion 22 which is branched off from thefirst waveguide core portion 21 obliquely are defined at an angle anddimension such that the optical signal guided from the optical fiber 3is not guided to the second waveguide core portion 22.

As a condition for this, the angle θ has to be an acute angle, which ispreferably 5° to 60°. By defining the angle in this way, almost theoptical signal guided from the common transmitting and receiving port 21a of the first waveguide core portion 21 is guided passing through thelinearly first waveguide core portion 21 to the receiving port 21 b.Further, the optical signal guided from the transmitting port 22 b iscoupled to the first waveguide core 21 in low-losses and guided to thecommon transmitting and receiving port 21 a.

A dimension of the branching portion 22 a of the second waveguide coreportion 22, namely a wide or thickness of the waveguide, is preferablysmaller than the first waveguide core portion 21 with a linearly shape.By making a width or thickness of the waveguide at the branching portion22 a smaller, it can prevent that the light signal guided from thecommon transmitting and receiving port 21 a of the first waveguide coreportion 21 is guided to the second waveguide core portion 22.

In an example shown in FIG. 1, the first waveguide core portion 21 andthe second waveguide core portion 22 are coupled so as to suppress ascatter of light, so that the second waveguide core portion 22 has agentle curved shape.

The respective waveguide core portions 21 and 22 are formed by materialwhich does not have absorption with respect to the used light and have ahigher refractive index with respect to the used light than the claddingportions 20 and 23. The waveguide core portions 21 and 22 are formed byepoxy resin, fluorinated polyimide or other polymer materials, forexample, and the material is added with an impurity to adjust therefractive index.

The cladding portions 20 and 23 are formed by material which does nothave absorption with respect to the used light and have a lowerrefractive index with respect to the used light than the waveguide coreportions 21 and 22. The cladding portions 20 and 23 are formed by epoxyresin, fluorinated polyimide or other polymer materials, for example,and the materials is added with an impurity to adjust the refractiveindex. Note that, the cladding portions 20 and 23 and the waveguide coreportions 21 and 22 may be formed by same materials or differentmaterials.

The optical fiber 3 is optically coupled at its one side to the commontransmitting and receiving port 21 a of the first waveguide core portion21 and mounted on the substrate 1. The optical fiber 3 may be amultimode fiber or a single mode fiber.

The light receiving element 4 is optically coupled at its receivingsurface to the receiving port 21 b of the first waveguide core portion21 and mounted on the substrate 1. The light receiving element 4 may bea photo diode, for example.

The light emitting element 5 is optically coupled at its emittingsurface to the transmitting port 22 b of the second waveguide coreportion 22 and mounted on the substrate 1. The light emitting element 5can be used with a semiconductor laser such as a fabry perot laser(FP-LD) and a distributed feedback laser (DFB-LD) etc.

Next, an operation of the optical transmitting and receiving moduleaccording to the present embodiment will be described with reference toFIG. 1.

A receiving optical signal which is incidence of light from the opticalfiber 3 is guided from the common transmitting and receiving port 21 ato the receiving port 21 b by the first waveguide core portion 21, andreceived by the light receiving element 4. The optical signal isconverted by the light receiving element 4 to an electric signal, andinput to a not shown receiving circuit which is connected to the lightreceiving element 4. In the above receiving operation, the receivingoptical signal which is guided by the first waveguide core portion 21 isnot guided to the second waveguide core portion 22 and the lightemitting element 5, so that the light emitting element 5 can transmit atransmitting optical signal at the same time.

Namely, in the receiving operation, the transmitting optical signalemitted by the light emitting element 5 is guided from the transmittingport 22 b to the branching portion 22 a by the second waveguide coreportion 22, coupled to the first waveguide core portion 21, guided tothe common transmitting and receiving port 21 a by the first waveguidecore portion 21, and coupled to the optical fiber 3. The secondwaveguide portion 22 branches off from the first waveguide core portion21 so as to make an acute angle θ with the receiving port 21 b, so thatthe transmitting optical signal is not guided to the light receivingelement 4 side and does not affect the receiving operation by the lightreceiving element 4.

The transmitting optical signal coupled to the optical fiber 3 is guidedby the optical fiber 3 and transferred to the outside of theoptoelectronic circuit device. Note that, wavelengths of the receivingoptical signal and the transmitting optical signal can be changed.

Next, an example of a method for producing the optical transmitting andreceiving module according to the present embodiment will be describedwith reference to FIGS. 1 and 2.

First, epoxy resin, fluorinated polyimide or other polymer material iscoated on the entire surface of the substrate 1 to form the claddingportion 20. Further, epoxy resin, fluorinated polyimide or other polymermaterial is coated on the entire surface thereof to form a highrefractive index layer to be the core portion. The difference of therefractive index of the cladding portion 20 and the high refractiveindex layer is adjusted by adding an impurity.

Then, the high refractive index layer is formed on its surface with aresist having the predetermined pattern by photolithography, andperformed with a reactive ion etching by using the resist as a mask toform the first waveguide core portion 21 and the second waveguide coreportion 22 having shapes shown in FIG. 1.

The resist is removed, and then epoxy resin, fluorinated polyimide orother polymer material is coated on the entire surface thereof so as tocover the waveguide core portions 21 and 22 to form the cladding portion23. As a result, the optical waveguide 2 which has the waveguide coreportions 21 and 22 embedded in the cladding portions 20 and 23 is formedon the substrate 1 as shown in FIG. 2.

Then, the optical fiber 3 is mounted on the substrate 1 so as to coupleone side of the optical fiber 3 with the common transmitting andreceiving port 21 a of the first waveguide core portion 21 optically.

Further, the light receiving element 4 is mounted on the substrate 1 soas to couple the receiving surface of the light receiving element 4 withthe receiving port 21 b of the first waveguide core portion 21optically. Furthermore, the light emitting element 5 is mounted on thesubstrate 1 so as to couple the emitting surface of the light emittingelement 5 with the transmitting port 22 b of the second waveguide coreportion 22 optically.

Next, effects of the optical waveguide and the optical transmitting andreceiving module according to the present embodiment will be described.

FIG. 3A is a view of a waveguide shape and FIG. 3B is a view of asimulation result of an intensity pattern of guided light in thereceiving operation by the optical waveguide shown in FIG. 3A. As shownin FIG. 3A, it is simulated about the optical waveguide that a length ofthe first waveguide core portion 21 with linearly shape is 7 mm and aninterval between the receiving port 21 b of the first waveguide coreportion 21 and the transmitting port 22 b of the second waveguide coreportion 22 is 250 μm. The respective waveguide core portions 21 and 22are assumed as 50 μm square and the difference with respect to therefractive index of the cladding portion is assumed as 1.5%. Note that,the X-coordinate and Z-coordinate indicate a position coordinate inwhich a shape of the optical waveguide is divided by a μm unit.

As shown in FIG. 3B, in the receiving operation, the receiving opticalsignal of 97.6% is guided to the receiving port 21 b of the firstwaveguide core portion 21 and the receiving optical signal of 0.0015% isguided to the transmitting port 22 b of the second waveguide coreportion 22. So the receiving optical signal almost goes straight in thefirst waveguide core portion 21 with the linearly shape. Therefore, thereceiving optical signal which is incident of light to the firstwaveguide core portion 21 is guided to the receiving port 21 b atlow-loss of 0.10 dB which is not more than 1.0 dB. Note that, anintensity of the optical signal which is guided to the second waveguidecore portion 22 is −28 dB, so that the optical signal is rarely guided.

FIG. 4A is a view of a waveguide shape and FIG. 4B is a view of asimulation result of an intensity pattern of guided light in thetransmitting operation by the optical waveguide shown in FIG. 4A. Theoptical waveguide shown in FIG. 4A is a same as FIG. 3A. Note that, inthe FIGS. 4A and 4B, the X-coordinate and Z-coordinate indicate aposition coordinate in which a shape of the optical waveguide is dividedby a μm unit.

As shown in FIG. 4B, in the transmitting operation, the transmittingoptical signal of 87.8% from the second waveguide core portion 22 iscoupled to the first waveguide core portion 21 and guided to the commontransmitting and receiving port 21 a. Therefore, the transmittingoptical signal from the second waveguide core portion 22 is guided tothe first waveguide core portion 21 at 0.57 dB in low-loss which is notmore than 1.0 dB.

As mentioned above, by the optical waveguide and the opticaltransmitting and receiving module according to the present embodiment,it can be realized that a transmitting operation and a receivingoperation is performed simultaneously in bi-direction by using a singleoptical fiber free from a wavelength selection filter or other opticalelement.

Further, the respective waveguide core portions 21 and 22 of the opticalwaveguide can be formed together by patterning etc. as mentioned aboveand a recess for inserting a wavelength selection filter or otheroptical element is not needed, so that the optical waveguide in low-losscan be produced in high yield. Namely, if a wavelength selection filteror other optical element is mounted, it may cause a deterioration of acharacteristic such as a light scattering loss and reliability of thecoupling strength.

The present invention is not limited to the above embodiment.

For example, materials for the substrate 1, the cladding portions 20 and23 and the waveguide core potions 21 and 22 which are included in theoptical waveguide are not limited and the material for the optical fiber3 is not also limited.

Other than the above, a variety of modification may be made within thescope of the present invention.

INDUSTRIAL APPLICABILITY

The optical waveguide and the optical transmitting and receiving modulein the present invention can be applied to an optical access system, forexample.

1. An optical waveguide comprising: a first waveguide having a commontransmitting and receiving port at one side and a receiving port at theother side, extending linearly, and able to guide an optical signal inbi-direction, and a second waveguide branching off from said firstwaveguide so as to make an acute angle with said receiving port,coupling said first waveguide at one side, having a transmitting port atthe other side, and guiding an optical signal to said first waveguide.2. An optical waveguide as set forth in claim 1, wherein said firstwaveguide is formed with a dimension able to guide a plurality of modeof the optical signal.
 3. An optical waveguide as set forth in claim 1,wherein said second waveguide is formed with a dimension of said oneside which is coupled to said first waveguide so as to make smaller thanthe other side.
 4. An optical transmitting and receiving module coupledwith an optical fiber, a light emitting element and a light receivingelement via an optical waveguide comprising: a first waveguide couplingsaid optical fiber at one side and a light receiving element at theother side and extending linearly, and a second waveguide branching offfrom said first waveguide so as to make an acute angle with said otherside of said first waveguide and coupling said first waveguide at oneside and a light emitting element at the other side.
 5. An opticaltransmitting and receiving module as set forth in claim 4, wherein saidfirst waveguide is formed with a dimension able to guide a plurality ofmode of said optical signal.
 6. An optical transmitting and receivingmodule as set forth in claim 4, wherein said second waveguide is formedwith a dimension of said one side which is coupled to said firstwaveguide so as to make smaller than said other side.